A Decentralized Dynamic Power Sharing Strategy for Hybrid Energy Storage System in Autonomous DC Microgrid

 

Abstract

Power allocation is a major concern in hybrid energy storage system (HESS). This paper proposes an extended droop control (EDC) strategy to achieve dynamic current sharing autonomously during sudden load change and resource variations. The proposed method consists of a virtual resistance droop controller and a virtual capacitance droop controller for energy storages with complementary characteristics, such as battery and super capacitor (SC). By using this method, battery provides consistent power and SC only compensates high frequency fluctuations without the involvement of conventionally used centralized controllers. To implement the proposed EDC method, a detailed design procedure is proposed to achieve the control objectives of stable operation, voltage regulation and dynamic current sharing. System dynamic model and relevant impedances are derived and detailed frequency domain analysis is performed. Moreover, system level stability analysis is investigated and system expansion with the proposed method is illustrated. Both simulations and experiments are conducted to validate effectiveness of the proposed control strategy and analytical results.

EXISTING  SYSTEM:

Droop control strategy is the mostly used decentralized method in MG. But existing droop based control methods only achieves proportional power sharing at steady state. Considering different dynamics of ESs, power sharing based on different frequency ranges is required.    The voltage-current characteristics of droop control scheme can be seen as a virtual resistor at the output of the converter. To decouple the power for ESs with different dynamics, this paper proposes an extended droop control method (EDC) by extending the concept of virtual resistance droop to virtual capacitance droop control. Then the proposed virtual capacitance droop controller can regulate ES with fast dynamics so that it only responds to fast fluctuation and will not provide power at steady state. The conventional virtual resistance droop remains for ES with slow dynamics for consistent power supply. Each ES operates at voltage regulation mode to maintain bus voltage and only local measurements are required for its converter controller without the communication with other ESs. The ESs can be located at different locations and system expansion can be flexibly achieved without the modification of existing control architectures.

PROPOSED SYSTEM:

The schematic diagram of an autonomous DC MG is  depicted in Fig. 1, which consists of PV, battery, SC and  various loads. PV panels are connected to DC bus through a boost converter and work at maximum power point tracking mode. DC load is connected to the bus. The hybrid battery/SC system will compensate power mismatch between PV and load to maintain bus voltage. Battery and SC are connected to the DC bus through their respective bidirectional

DC/DC  

 

CONCLUSION:   

This paper proposes a decentralized control strategy for dynamic current sharing in HESS. Output voltage characteristics of the battery and SC are regulated by a virtual resistance droop controller and a virtual capacitance droop controller respectively. The proposed droop controllers inherently act as a LPF for battery and an HPF for SC to load response so that SC compensates high frequency fluctuations during transient and battery provides load power at steady state. For practical implementation of this control strategy, a detailed procedure for parameter design is proposed. With the developed system dynamic model and derived transfer functions, parameters can be properly designed to ensure stable operation, bus voltage regulation and dynamic current sharing. System expansion is also demonstrated to show the scalability of the proposed method. Simulations and experiments are conducted to validate effectiveness of the proposed control strategy and analytical results.

 

REFERENCES

[1] D. E. Olivares, A. Mehrizi-Sani, A. H. Etemadi, C. A. Canizares, R.  Iravani, M. Kazerani, A. H. Hajimiragha, O. Gomis-Bellmunt, M. Saeedifard, R. Palma-Behnke, G. A. Jimenez-Estevez, and N. D. Hatziargyriou, “Trends in Microgrid Control,” IEEE Trans. Smart Grid, vol. 5, no. 4, pp. 1905–1919, Jul. 2014.

[2] N. Hatziargyriou, H. Asano, R. Iravani, and C. Marnay, “Microgrids,” IEEE Power Energy Mag., vol. 5, no. 4, pp. 78–94, 2007.

[3] A. T. Ghareeb, A. a. Mohamed, and O. a. Mohammed, “DC microgrids and distribution systems: An overview,” in 2013 IEEE Power & Energy Society General Meeting, 2013, pp. 1–5.

[4] Y. Gu, X. Xiang, W. Li, and X. He, “Mode-Adaptive Decentralized Control for Renewable DC Microgrid With Enhanced Reliability and Flexibility,” IEEE Trans. Power Electron., vol. 29, no. 9, pp. 5072–5080, 2014.

[5] A. Khorsandi, M. Ashourloo, and H. Mokhtari, “A decentralized control method for a low-voltage dc microgrid,” IEEE Trans. Energy Convers., vol. 29, no. 4, pp. 793–801, 2014.

[6] T. Dragicevic, X. Lu, J. Vasquez, and J. Guerrero, “DC Microgrids-Part I: A Review of Control Strategies and Stabilization Techniques,” IEEE Trans. Power Electron., vol. 8993, no. c, pp. 1–1, 2015.

[7] N. R. Tummuru, M. K. Mishra, and S. Srinivas, “Dynamic Energy Management of Renewable Grid Integrated Hybrid Energy Storage System,” IEEE Trans. Ind. Electron., vol. 62, no. 12, pp. 7728–7737, 2015.

[8] J. Xiao, P. Wang, and L. Setyawan, “Hierarchical Control of Hybrid Energy Storage System in DC Microgrids,” IEEE Trans. Ind. Electron., vol. 62, no. 8, pp. 4915–4924, Aug. 2015.

[9] J. Shen and A. Khaligh, “A Supervisory Energy Management Control Strategy for a Battery/ Ultracapacitor Hybrid Energy Storage System,” IEEE Trans. Transp. Electrif., vol. 7782, no. 1, pp. 1–1, 2015.

[10] J. Li, Y. Liu, S. Wang, J. Shi, L. Ren, K. Gong, and Y. Tang, “Design and advanced control strategies of a hybrid energy storage system for the grid integration of wind power generations,” IET Renew. Power Gener., vol.